Circumcision: there goes the microbial neighbourhood

A flap of foreskin isn’t the only thing missing after a circumcision. Microbes that call the penis home disappear, too, which could explain why the procedure reduces a man’s chance of contracting HIV.

“The microbes change dramatically,” says Lance Price, a microbiologist at the Translational Genomics Research Institute in Flagstaff, Arizona, whose team identified thousands of microbes on the penises of 12 HIV-negative men. All had participated in a clinical study in Uganda which showed that circumcision halves the chances of getting the virus.

The team discovered a total of 38 families of bacteria on the men’s penises before circumcision, and 36 a year after. But the make-up of these communities had swung. Gone were a diverse population of bacteria intolerant of oxygen and linked with vaginal infection; now there was a more homogenous air-loving lot, more typical of other patches of skin.

Price thinks that some of the expelled bacteria provoke an immune reaction on an uncircumcised penis, causing specialised immune cells to shuttle HIV throughout the body.

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Residents of the penis

Even where religion, culture or costs prevent widespread circumcision, Price says the work could be a first step in delivering the benefits of the procedure without surgery. “The really interesting thing about this study is the potential to modify somebody’s risk for HIV.”

His team next plans to determine which microbes are most common on the penises of men who go onto to acquire HIV. Targeting these bacteria with antibiotics – while leaving harmless or even helpful residents of the penis alone – could stem the spread of HIV, he says.

Martin Blaser, a microbiologist at New York University, says the new study is the most comprehensive look yet at the microbes living on the penis. But given that microbial populations on other parts of the body shift over time, he wonders whether the pre-circumcision bacteria will return. “I expect it will stay changed,” he says.